It has long been appreciated that one of the more desirable attributes of a piano is that the amplitude of the tones provided by the piano are each separately under the control of the respective finger of the player, immediately as sounded. Thus, a piano even when used as a single voiced instrument is nevertheless capable of expressing shades of dynamic control unattainable in other keyboard instruments such as organs or harpsichords.
One early instrument, the clavichord, did have the ability to affect pitch to a limited extent after the key has been depressed. Since the key contacts the string via a tangential contact element during the time that the note is held, extra finger pressure can cause the note to become sharp while the string is vibrating.
Historically, dynamic control in organs has been achieved through the use of a foot pedal, for example, but the control thus provided is comparatively coarse and usually applies to all notes sounded simultaneously at a given time. Organs and other instruments operated by keys or a keyboard are today frequently electronic in nature, i.e., the various tones are generated by electronic means and the tones are switched electrically by manipulation of the keys, the ultimate output of the instrument being produced typically at one or more audio speakers. Attempts have been made to endow such instruments with touch sensitivity in order to expand the dynamic capabilities of the instrument, but such efforts, when successful, have involved a fairly complex and usually very expensive system. For example, it is known that strain gauges, electromagnetic transducers, and piezoelectric crystals can be employed inasmuch as they tend to produce an output which varies with pressure. However, the use of such devices is expensive and requires complex auxiliary electronic circuitry.
The mechanical linkage in instruments such as the piano is also complex and relatively expensive, and has the disadvantage that it can only produce percussive effects proportional to finger velocity when the key is first depressed, since the hammer which contacts the string is designed to fall away from the string after initially striking the string.
Moreover, prior art electronic musical instruments do not provide touch-sensitive audio filters wherein a filter may preferably be associated with each key of the instrument. A typical known instrument comprises, inter alia, a keyboard and corresponding voltage divider, control circuitry, envelope generator and voltage controlled oscillators. These instruments may provide some degree of touch-sensitive amplitude control but usually discrete control associated with each and every key is not practical as the cost is prohibitive. Also, with these instruments direct touch-responsive filtering has not been used. Usually the applied pressure is converted to a voltage which is then used to control voltage-controlled filters or voltage-controlled amplifiers. A voltage-controlled filter is relatively expensive. Furthermore, the inclusion of resistive voltage dividers, relatively complex control circuitry and envelope generators adds significantly to the overall cost of the instrument.